Failed to restart TFTP issue

[richard_chen]

(2017-07-24 09:06)NiKiZe Wrote:  You should never have more then one DHCP server per network.
Some DHCP servers has redundancy options so that they can work together, but you should never have multiple offers like that.

You can have one DHCP server and one ProxyDHCP but that's different.

For information about how the Microsoft DHCP can be configured see the first part of http://ipxe.org/appnote/chainload_wds and http://ipxe.org/howto/msdhcp

Considering that if there is only one server, if a fault occurs, it will cause the production line to stop, so we use multiple DHCP servers to assign different IP scope. we use this solution for WDS and iPXE long time.
Current this issue only happend with USB LAN card, production with lots of units and more than one DHCP, If any of these three conditions is missing, this issue also can not been duplicated, these units have no onboard LAN, so we must use USB LAN card. We also cannot split the network, because have no lots of procution server. so current used one DHCP&iPXE server for short time solution. However, this solution poses a risk of stopping production.
The point of this issue is why it always send DHCP request when DHCP reply ACK? and why it always repeat this stepping and not begin to go next stepping for TFTP undionly.kpxe?